1. Technical Field
The present disclosure relates to variable gain multistage amplifiers and receivers.
2. Description of the Related Art
In the past, as a low noise amplifier (LNA), a variable gain amplifier that can change the gain at the time of amplification of a signal has been known.
As the existing variable gain amplifier, a variable gain amplifier provided with a first cascode amplifier, a second cascode amplifier, and a gain adjusting section has been known. The first cascode amplifier includes a first common source transistor and a first common gate transistor. The second cascode amplifier makes a differential pair with the first cascode amplifier and includes a second common source transistor and a second common gate transistor.
The gain adjusting section has one end connected to the drain of the second common source transistor and the source of the second common gate transistor and the other end connected to the drain of the second common source transistor and the source of the second common gate transistor. Moreover, the gain adjusting section includes a transistor pair that is opened and closed by a control bias voltage and a resistance (see, for example, Japanese Unexamined Patent Application Publication No. 2006-109409).
Furthermore, a variable gain amplifier of Japanese Unexamined Patent Application Publication No. 2006-109409 performs gain adjustment by changing the impedance between differentials.
Moreover, the existing variable gain amplifier is provided with an amplifying element, a load, an output terminal, a bias circuit, a variable current source, a gain detecting circuit, and a direct-current output voltage detecting circuit. The amplifying element includes a control electrode, a grounding electrode, and an output electrode. The load is connected to the output electrode of the amplifying element. The output terminal is formed at a connecting point between the output electrode of the amplifying element and the load.
The bias circuit is connected to the control electrode and is a circuit for controlling the gain of the amplifying element. The variable current source is connected to the output electrode and is a power supply for controlling the direct-current output voltage at the output terminal. The gain detecting circuit is connected to the output terminal and detects the gain of the amplifying element. The direct-current output voltage detecting circuit is connected to the output terminal and detects a direct-current output voltage. Moreover, the bias circuit is controlled by the output of the gain detecting circuit. The variable current source is controlled by the output of the direct-current output voltage detecting circuit (see, for example, Japanese Unexamined Patent Application Publication No. 2003-234629).
Furthermore, the variable gain amplifier of Japanese Unexamined Patent Application Publication No. 2003-234629 changes the gain by control of the gate potential of the source grounding amplifier circuit.